A counterflow process is a common technique to extract soluble compounds from solids, such as to extract flavor, aroma and caffeine compounds from coffee grounds. Counterflow systems are often characterized as those having two flows of different compounds, e.g., some combination of gases, liquids and solids, traveling in opposite directions (or holding one stationary while the other flows around or through it). They can be designed to maximize the exchange of certain properties (e.g., heat or dissolvable solids concentration) from one flow or compound to the other and they achieve this by maintaining an essentially constant gradient between the two over the entire length of the flow system. For example, in a counterflow coffee extraction system, the difference in concentration of certain desirable dissolvable solids between a solvent (e.g., water) and a solid (e.g., coffee grounds) remains generally similar from one end of the extraction column or system to the other. In parallel flow systems, the gradient between the two is often initially very high, but drops off quickly along the length of the flow path.
Traditional counterflow processes for some compounds, e.g., coffee extraction, can be negatively affected by uncontrolled conditions such as under extraction (e.g., which can result in loss of revenue), over extraction (e.g., hydrolysis of cellulose fibers leading to bitter taste and shelf unstable extracts), inadequate column length (e.g., inadequate total dissolved solids (“TDS”) leading to the need for concentrating post extraction), and/or plugged column(s) (e.g., which can cause a loss of flow, revenue loss and excessive extraction times).
Many such extraction systems can be difficult to load, unload and/or clean. For example, some extraction systems can leave behind a slurry of wet grinds that needs to be de-watered post-extraction prior to disposal and/or reuse elsewhere as fuel or nutrients or landfill. Extraction columns can be wet-flushed, but this process requires re-wetting the spent grinds, which can make evacuation easier, but at the expense of producing wet, spent grinds that need additional processing to become recyclable (e.g., into fuel or soil nutrients).
Many extraction systems are of either the batch type or the continuous type, and typically offer the operator limited options while processing desired extracts (e.g., in terms of TDS and volume). None of the current systems are versatile enough to provide most of the benefits of both the batch and continuous type and with a selectable column length that is both heatable and coolable.
Many extraction systems are also often unable to simply bypass areas of the extraction column that are either spent or plugged or have developed channel flows. These systems typically offer less than optimal control of the various aspects of extraction, including being in control of contact time, temperature, pressure, dry spotting, and/or under or over extraction.
Some extraction methods are based a cold extraction process where ground coffee is simply soaked in cold water while held in a cloth sack for an extended time period. This method is microbially unstable, and the resulting cold brew coffee has a taste that is quite different from hot brewed coffee, which is often the standard to be met.
Some extraction methods may use a solvent that is too hot, resulting in, for example, breakdown (e.g., hydrolysis) of the cellulose present in a coffee bean and/or inclusion of the coffee bean's woody fiber in the extract.